Microelectronic devices are manufactured on a substrate made from silicon or other suitable semiconductor materials. In typical fabrication processes, several hundred microelectronic devices are fabricated on a single wafer at the same time. Each microelectronic device has numerous electrical circuits formed from layers of device features that are integrated together on the front side of the wafer substrate. The integrated circuits are formed by masking, doping, depositing, and selectively removing materials in very precise patterns on the front side of the wafer substrate. During the fabrication of the integrated circuits on the front side of the wafer substrate, undesirable waste materials often accumulate on the backside of the substrate.
In the highly competitive semiconductor industry, it is desirable to maximize the throughput of finished microelectronic devices. Current semiconductor manufacturing processes are expensive because, among other reasons, the device features of the integrated circuits may be as small as 0.35 to 0.50 .mu.m, and many of the process steps are performed in extremely clean environments. Therefore, to reduce the unit cost of making each microelectronic device, it is desirable to maximize the number of finished dies produced in a period of time.
One factor influencing the throughput of semiconductor manufacturing is that the waste matter on the backside of the wafer should be removed to prevent the wafers from warping and to provide a clean surface for extrinsic gettering of the wafer substrate. The waste matter may consist of several layers of material used to form some of the components of the circuits on the front side of the substrate. Typically, the waste matter is made from layers of polysilicon, tungsten, aluminum, metal oxides, borophosphate silicon glass ("BPSG"), or tetraethyl orthosilicate ("TEOS"). The waste matter on the backside of the wafer may cause the silicon wafer to warp because internal stresses in the lattice structures of the waste matter tend to bend the thin, flexible silicon wafer. Additionally, because the materials on the backside of the wafer have different rates of thermal expansion than silicon, additional stresses act on the wafer substrate as the wafer is heated and cooled throughout the fabrication process. Thus, to prevent the wafer substrate from warping and to provide a clean backside for other processes, it is desirable to remove the waste matter from the backside of the wafer.
One problem with conventional fabrication processes is that removing the waste matter from the backside of a wafer reduces the throughput and increases the material costs of the finished microelectronic devices. In conventional fabrication processes, waste matter is removed from the backside of the wafer by: (1) depositing a sacrificial cover layer made from a resist material over the front side of the wafer to protect the circuitry on the front side from the etchants used to remove the waste matter; (2) etching the waste matter from the backside of the wafer using suitable etchants that remove the particular materials of the waste matter; and (3) removing all of the sacrificial resist layer from the front side of the wafer. Conventional waste matter removal methods require additional process steps and time because the sacrificial resist layer must be deposited over on the front side of the wafer and then completely removed from the wafer. This method wastes time and material because the sacrificial resist layer is a temporary layer formed on the wafer only for the purpose of removing material from the backside of the wafer. Since the sacrificial resist layer is not used for any other purpose, the time and materials used to form and remove the sacrificial resist layer are lost expenses once the backside of the wafer is clean. Thus, conventional methods for removing the waste matter from the backside of the wafer reduce the throughput and increase the material cost of manufacturing microelectronic devices.
In light of the problems with conventional methods for removing waste matter from the backside of a wafer, it would be desirable to develop a method for removing waste matter from the backside of the wafer that does not markedly increase the time and materials required to fabricate microelectronic devices on semiconductor wafers.